Cathode-ray tube



Nov. 16, 1943. c. s. SZEGHO 2,334,516

CATHODE RAY TUBE Filed May 1:5, 1942 'oiZsMiLZzMS fl R ATTORNEY Patented Nov. 16, 1943 T D STATES PATENT OFFICE- cATHopE-RAY TUBE Constantin S. Szegho, New York, N. Y., assignor" I to 'The Rauland Corporation, Chicago, 111., a.

corporation of Illinois Application May 13, 1942, Serial No. 442,839

4 Claims. ('01. 250 141),

This invention relates to new and useful improvements. in cathode ray tubes and more particularly in tubes of thekind in which an image traced on a fluorescent screen by the electronic beam is projected through a window facing the activated surface of the screen, the so-called front projection type of tube.

' In front projection tubes most of the wall of the tube envelope is coated with a conducting layer such as colloidal carbon, leaving clear only the window through which the optical image is viewed or projected. Whenpotentials of the order of kv. are employed theglass window tends to acquire an electrical charge from stray electrons which produces undesired deflections The potential may be applied to a conductive I coating or lines of conducting material on or nearthe window so as to reduce any possibility of an undesired potential difference occurring at any portion of the window or portion of the window and the surrounding wall.

The lines may be of colloidal graphite or liquid silver, or the window may be coated with a thin,

is exposed to an electron beam produced by an,

electron gun 4 in-neck 5 of the envelope.

In-the construction shown in Fig. 1 lines 6 of conducting material are marked on the window 2; in the construction shownrin Fig. 2 a wire mesh .1 is provided behind the window. The conductive protection li or I is connected withthe inside conductive coating or the screen of the structure.

In Fig. 3 the elements corresponding to the other figures are designated by the same reference numerals. V2 is the potential of a conducting coating on the wall of envelope l which is transparent layer of metal, for example metallic fluoride or the like preferably of such thickness that it reduces light reflections of the glass surface, or the conducting material may be incorporated in the window itself. The graphite or liquid silver may be first applied completely to cover the window and then most of it removed by ruling or similar process.

The lines thus formed on the window do not appreciably diminish the brightness of the observed image and since they are not in the focal plane of any optical system employed for the projection of the image on a viewing screen, the lines do not produce visible shadows.

Alternatively, a wire mesh may be provided between the window and the fluorescent screen in close proximity to the window and Connected to the anode of the tube.

In the drawing Fig. 1 is a front view. of one embodiment and Figs. 2 and 3 side elevations of two other embodiments of the invention.

The envelope is designated by the reference numeral lwhich is coated on the inside with colloidal graphite exceptfor a window 2 made up of optically flat glass. The envelope encloses a fluorescent screen 3 opposite the window 2 which recent screen. i CONBIANTIN s. szsono. a,

connected with the grid work of lines 5 onwindow 2. This potential is different from the potentials V1, V3 and V4, the potentials of the first anode, the intermediate wall coating and the wall a coating connected with the screen 3.

What I claim is: i 1. In a cathode ray tube, a fluorescent scree an electron gun arranged to project a beam of electrons on a surface of said screen, an evacuated envelope enclosing said screen and gun, a coating of conductive material on the inside of said envelope connected with said screen, a window ofjoptical flat glass in said envelope opposite saidscreen, and conductors on' said window facing said screen for keeping the electrical potential of the window at a substantially fixed level with respect to the fluorescent screen.

2. In a cathode ray tube, a fluorescent screen, an electron gun arranged to project a beam of electrons on a surface of said screen, an evacuated envelope enclosing said screen and gun, a window of optical flat glass'inv said envelope opposite said screen, and a coating of metallic fluoride on said'window for keeping the electrical potential of the window at a fixed level with respect to the fluorescent screen. 1

- 3. The. cathode raytube, a fluorescent screen; an electron gun arranged to-project a beam 01. electrons on a surface of said screen, an evacuated envelope enclosing said screen and'gun, a window of optical flatglass in said envelope opposite said screen, and lines of conducting material on said window for keeping the electrical potential of the window-at a fixed level spect to the fluorescent screen. V

4. In a cathode ray tube, a fluorescent screen,

With rean electron gunarranged to project a beam of electrons on a surface of said screen, an evacuated envelope enclosing said screen and'gun, a,

window of optical flat glass in said envelope opposite said screen, and conducting material incorporated in said window connected withsaid screenfor keeping the electrical potential of the respect to the fiuo-.

window at a fixed level with 

